| Summary: | Laser induced fluorescence (LIF) studies have been performed on the transition
metal-containing free radicals nickel cyanide (NiCN), niobium oxide (NbO), niobium
methylidyne (NbCFf) and tantalum methylidyne (TaCH). All molecules were produced by
the reaction of laser-ablated metal atoms with a reactant gas under supersonic jet-cooled
conditions.
Precise rotational constants and bond lengths have been obtained for the X₁²Δ[sub 5/2] state
of NiCN. The vibrational structure "of this state is dominated by a Fermi resonance
interaction, as are those of the low-lying X₂²Δ[sub 3/2] and W₁²Π[sub 3/2] states. Four excited electronic
states have been identified, showing that the electronic structure of NiCN is remarkably
similar to that of NiH.
High resolution spectra of NbO have given the rotational and hyperfine constants for
the levels v=0-3 of the B⁴Π state. Strong irregularities in the vibrational dependences of
these constants can be interpreted in terms of spin-orbit interaction between the B⁴Π state
and the f²Π , e²Φ and d²Δ states. The hitherto unknown ⁴Δ state is estimated to lie near 17500
cm⁻¹, from the vibrational dependence of the spin-rotation parameter γ of the B⁴Π state.
Thorough vibrational, rotational and hyperfine analyses were performed on the X³Δ[sub I]
state of NbCH. The hyperfine widths of this state vary considerably as a result of spinuncoupling.
The A³Φ₂ and B³Δ₁ excited states are heavily perturbed, with as many as nine
levels appearing where only one is expected, which complicates the vibrational and rotational
analyses.
Tantalum methylidyne was found to have an X Ω=0⁺ (¹Σ⁺) ground state, with bond
lengths r₀(Ta-C)=1.7714 Å and r0(C-H)= 1.080 Å. The rotational lines exhibit unusually
large quadrupole hyperfine splittings caused by the nuclear spin, 1=7/2, of the ¹⁸¹Ta nucleus.
This effect is normally too small to appear in optical spectra. Interaction between the A Ω=1
(¹Π) and B Ω=0+ (³Π₀[sub +]) states has been identified through the transfer of magnetic hyperfine
character to the B state from A.
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